1. Field of the Invention
The present invention is directed towards a method and apparatus for providing a safe, precise, and cost-effective storage tank leak detection system and more particularly, to a method and apparatus wherein the containment integrity of a storage tank is determined by mass measurements of the stored product.
2. Background Information
Storage tanks play a vital role in today's economy. The economy, on a global scale, depends on the proper function of these tanks as they are prevalent in several industries and virtually every geographical region in the world. In light of the vital role these storage tanks play, the integrity of the tanks is placed at a premium. That is, storage tank owners are willing to invest huge sums of money in both the maintenance and inspection of such tanks.
These tanks come in all shapes and sizes, are found both below and above ground, and are used to store a wide range of materials. Storage tank capacities range from hundreds to millions of gallons and are used to store a staggering assortment of products; these storage tanks are commonly used to store hazardous material.
As one could imagine, there are a wide range of problems associated with maintaining storage tank integrity, particularly with above ground storage tanks. Given the enormous dimensions of above ground tanks, the corrosive products contained within the tanks, the incredible mass of the stored product, and the extreme weather conditions the tanks are subjected to, it is plain to see that above ground storage tank leaks are an all-to-common problem. Using the United States Environmental Protection Agency leak detection threshold criteria of 0.05 gallons per hour in a 10,000-gallon underground tank, that threshold would equate to a 15 gallon per hour detection level in an 80,000 barrel above ground tank. Given the limited number of systems capable of meeting the EPA's underground storage tank leak detection threshold and the added difficulties associated with above ground tanks, the difficulty in protecting against and detecting leaks is easily seen.
However, the recognized difficulty in preventing storage tank leaks does not mitigate the duties or liabilities imposed on responsible parties. Tremendous environmental and economic consequences and the threat of litigation and clean up costs associated with storage tank leaks force responsible parties to invest large sums of money in the maintenance and inspection of the tanks. Tank inspections are costly with respect to the amount of money spent, the danger presented to the inspectors and the environment, and production downtime. In fact, these inspections often remove a tank from service for more than one month. The threat of liability also forces responsible parties to spend money unnecessarily for the maintenance of these tanks. Moreover, liability does not end with litigation and clean-up costs.
Currently, responsible parties are, in some countries, being incarcerated as a direct result of storage tank leaks. These leaks have contaminated surrounding ground water, some of which serves as drinking water for local residents. As such, the facilities associated with such incidents have been shut down until compliance with emissions regulations can be established beyond reasonable doubt. Such proof, in turn, is dependent on proof of reliable and sufficiently accurate detection systems and methods for proving such compliance. Each day the shuttered facilities remain inoperative adds to an already tremendous amount of money lost.
Prior to the present invention (to be described in detail hereafter), there are simply no known systems or methods by which the leak detection requirements can be met. Presently available leak detection systems lack detection thresholds low enough to detect leaks down to permissible upper leakage limits for above ground storage tanks.
Clearly, for the reasons set forth above, there is a dire and immediate need for the ability to determine, with far more precision than presently possible through use of presently available systems and methods, the presence and degree of leakage from above ground storage tanks, at least to the extent of proving compliance with applicable storage tank leakage regulations or statutes.
Related Conventional Technologies and Distinctions from Present Invention
Storage tank leak detection systems are known in the art; however, these products are fraught with problems. The present systems are imprecise, or provide erroneous data for any or all of reasons including: the consistency of the
soil acting as the tank's foundation, the temperature stratification of the in-tank product, extraneous noise sources, thermal expansion of the tank's contents, water table level, previous soil contamination, and/or tank shell dynamics.
Further, some detection devices can only be used when the storage tank is empty, and no known system or method ensures a comprehensive inspection of the tank. The most common form of such a system is “vacuum box testing,” however, this system is intended only for weld joints and is not usually applied to the entire tank bottom. Magnetic flux floor scanning is also used, but is not effective at examining the area of the floor surface close to the surface walls or where there are physical obstructions. Ultrasonic detection is used, but this is only effective for small areas of the surface. Gas detection is also used, but the types of materials stored in the tank can obstruct this method.
Other common leak detection systems employ a level sensor. However, even large volume changes produce only small level changes, as the cross-sectional area of the liquid surface in these tanks is very large. This, combined with differential expansion and temperature change of the stored liquid and its vapor, make this type of detection system inconsistent and very nearly worthless.
Finally, mass measurement detection systems are known in the art. However, the presently available systems and associated methods are not capable of the precision, which is indicated above as crucial at the present time (and which, as described below, is afforded by the systems and methods of the present invention). Present mass measurement leak detection systems in the art
are limited by tank shell variations resulting from temperature effects on tank shell plating. As such, known mass measurement detection systems are only sensitive enough to be used in smaller tanks, typically underground storage tanks. However, as will be seen in the specification to follow, the present invention overcomes tank shell variations and other shortcomings of presently known technology in this field through data collection and data correction apparatus, techniques and interpretation.
In light of the severe consequences of failing to detect significant storage tank leaks, presently not detectable through use of known systems or methods, there is a compelling need for a system and method by which one can detect very small leaks even in very large tanks, ideally in a safe and cost effective manner.
It would well serve those who are responsible for maintaining storage tank integrity to provide a safe, precise, and cost-effective detection system that does not depend on independent variables such as fluid temperature, fluid stratification, or tank stabilization, and may be used in an efficient manner thereby preserving industrial and environmental resources.
The system by its very nature is also a very effective means of accurately measuring the amount of fluid (product) added to or removed from a tank. Accordingly the system represents an attractive alternative to hand strapping and other volume based (through flow meter) product custody transfer measurement methods and apparatus. Where the accuracy of custody transfer measurements is of significance due to the quantities, commercial terms and value of the product this system can be directly employed to accurately measure the transfer amounts.